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HIGH FREQUENCY VENTILATION - NEONATES

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HFV- how, what , when ,why?
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HIGH FREQUENCY VENTILATION - NEONATES

  1. 1. HIGH FREQUENCY VENTILATION Dr. ADHI ARYA SENIOR RESIDENT –GMCH -32 CHANDIGARH
  2. 2. • INTRODUCTION • MECHANISM OF VENTILATION • WHY HFV • TYPES OF HFV • USES • TERMINOLOGY AND SETTINGS( INITIATION AND WEANING OFF) • MONITORING/ROUTINE CARE ON HFV • COMPLICATIONS • EVIDENCE
  3. 3. INTRODUCTION HFV is a type of mechanical ventilation that uses a constant distending pressure (mean airway pressure [MAP]) with pressure variations oscillating around the MAP at very high rates This creates small tidal volumes, often less than the dead space. HFOV relies on alternative mechanisms of gas exchange such as molecular diffusion, Taylor dispersion, turbulence, asymmetric velocity profiles, Pendelluft, cardiogenic mixing and collateral ventilation
  4. 4. NATURAL HIGH FREQUENCY VENTILATION • HUMMINGBIRD • DOG’S PANTING
  5. 5. MECHANISM OF ACTION •ALVEOLAR VENTILATION = (Vt-Vd) * RATE • IN HFV Vt< Vd, so actualluy no ventilation should occur
  6. 6. HFV Provides augmented gas distribution by means of numerous gas transport mechanisms.  Convection ventilation( bulk flow)  Pendalluft effect  Taylor dispersion  Asymmetric velocity profiles  Cardiogenic Mixing  Molecular diffusion  Collateral Ventilation
  7. 7. Convection, Transit Time and Direct Ventilation Convection  is the transport of air flow at a constant equal velocity that is parabolic in shape. TO SHORT PATH LENGTH UNITS THAT BRANCH OFF FROM PROXIMAL AIRWAYS
  8. 8. Pendalluft Effect At the end of expiration: • Alveoli with short time constants (fast alveoli units) are empty. • Alveoli with longer time constants (slow alveoli units) are still emptying Asynchronous filling: • Gases will move from slow units to fast units because of pressure gradients between the alveoli. Asynchronous Filling
  9. 9. Taylor Dispersion The relationship between:  Axial velocity profile (Turbulence)  the diffusion of gases in motion  and the branching network of the lungs.
  10. 10. Asymmetry Airflow moving through the airways moves in a u-shape formation. At the center of the lumen air will move at a faster velocity, than air that is closest to the wall. Asymmetry Occurs with rapid respiratory cycles. Gases (O2) at the center of the lumen will advance further into the lungs as gases (CO2) along the wall of the airway moves out towards the mouth.
  11. 11. • Asymmetrical Velocity Profiles • Inspiration • The high frequency bulk flow creates a “bullet” shaped flow profile, with the central molecules moving further down the airway than those molecules found on the periphery of the airway. • Expiration • The velocity profile is blunted so that at the completion of each return, the central molecules remain further down the airway and the peripheral molecules move towards the mouth of the airway
  12. 12. Cardiogenic Mixing As the heart beats the heart provides additional peripheral mixing by exerting pressure against the lungs during contraction of the heart. This pressure promotes the movement of gas flow through the neighboring parenchymal regions.
  13. 13. Collateral VentilationMolecular Diffusion Maintaining a constant distending pressure with HFV within the lungs along with movement of gas molecules promotes gas diffusion across the alveolar membrane, at a faster rate. Collateral ventilation increases with HFV due to connections between the alveoli  (Pores of Kohn)
  14. 14. WHY HFV THEORITICAL ADVANTAGES • SMALL TIDAL VOLUMES limits alveolar over distension • HIGHER MAP Better alveolar recruitment • CONSTANT mPaw during inp and exp preventing end alveolar collapse
  15. 15. Volume Pressure Zone of Overdistention Safe window Zone of Derecruitment and atelectasis Goal is to avoid injury zones and operate in the safe window HFOV is used to prevent Ventilator Induced Lung Injury
  16. 16. Pressure and Volume Swings INJURY INJURY CMV HFOV  During CMV, there are swings between the zones of injury from inspiration to expiration.  During HFOV, the entire cycle operates in the “safe window” and avoids the injury zones.
  17. 17. TYPES OF HFV Based on characteristic of exhalation (Active /Passive/ Hybrid )and source of generation – 3 types 1. HFPPV 2. HFJV 3. HFOV
  18. 18. USES 1. failure of conventional ventilation in the term infant (Persistent Pulmonary Hypertension of the Newborn [PPHN], Meconium Aspiration Syndrome [MAS]).4,5 2. Air leak syndromes (pneumothorax, pulmonary interstitial emphysema [PIE])7 3. Failure of conventional ventilation in the preterm infant (severe RDS, PIE, pulmonary hypoplasia) or to reduce barotrauma when conventional ventilator settings are high. 4. Lung hypoplasia syndromes
  19. 19. TERMINOLOGY
  20. 20. Oxygenation Depends on 1) MAP 2) Fio2
  21. 21. Ventilation Depends on 1. amplitude( depth of oscillations around MAP) 2. Frequency 3. Ti
  22. 22. • CMV ALVEOLAR VENT = FREQ * TV •HFV ALV VENT= F*TV2
  23. 23. More TV in 6 Hz Cycle as compared to 8 Hz
  24. 24. INITIAL SETTINGS DEPENDS ON PATHOLOGY • OPTIMAL LUNG VOLUME STRATEGY • LOW VOLUME STRATEGY
  25. 25. • SEVERE RESPIRATORY FAILURE One-study sites that 50% of infants studied who met the criteria for ECMO were successfully managed with HFV alone. • Initially, start with a MAP 2 cm higher than with conventional ventilation and incrementally increase it. Very high MAPs may be needed to achieve adequate oxygenation.
  26. 26. • PERSISTENT PULMONARY HYPERTENSION • Hyperventilate to achieve a PaCO2 of 25-35 Torr with a pH of 7.45-7.55. Some literature suggests a pH of 7.55-7.65. • Hyperoxygenate generally by maintaining the FIO2 at 1.0. Increase the MAP to maintain adequate oxygenation
  27. 27. LUNG HYPOPLASIA SYNDROMES • Initially use the same MAP as on conventional ventilation then aggressively increase in 1cm increments to optimum lung volume. • Adjust the amplitude to give a PaCO2 of 45-50.
  28. 28. • AIR LEAK SYNDROMES • • Initially set the MAP 1-2 cm H2O below the MAP on conventional mechanical ventilation.
  29. 29. WEANING
  30. 30. COMPLICATIONS • HYPOTENSION ( Increased intrathoracic pressure -- decreased VR) • AIRLEAKS • IVH/PVL • NECROTISING TRACHEOBROCHITIS
  31. 31. MONITORING 1. SEDATION 2. AUSCULTATION 3. CXR (1hr after initiation or any change in settings/deterioration) 4. SUCTIONING 5. BP MONITORONG
  32. 32. SUSTAINED INFLATION lung recruitment maneuver. • There are several ways in which to perform a SI maneuver. • In our institution, the piston is paused (thus leaving the patient in CPAP) and the Paw is increased by 8-10 cm H2O for 30-60 seconds. • Once the SI maneuver is completed, the piston is restarted. • Potential complications: • Pneumothorax • CV compromise / altered hemodynamics
  33. 33. When To Utilize A SI Maneuver • When initiating HFOV to recruit lung • After a disconnect or loss of FRC/Paw • After suctioning (even with a closed suction system) • Inability to wean FiO2 • When considering increasing Paw • A recruitment maneuver may recruit lung allowing you to maintain the baseline Paw and, thus, not increase support.
  34. 34. EVIDENCE ( should answer these three questions)
  35. 35. EVIDENCE
  36. 36. PULMONARY OUTCOMES OF CONTROLLED TRIALS OF HFV DURING SURFACTANT ERA AND SYNCHRONOSED VENTILATION
  37. 37. AS PRIMARY MODE • AS A PRIMARY MODE Elective high frequency ventilation compared to conventional mechanical ventilation in the early stabilization of infants with respiratory distress - Cochrane-March 2015 Insufficient evidence exists to support the routine use of high frequency oscillatory ventilation instead of conventional ventilation for preterm infants
  38. 38. AS RESCUE THERAPY • Preterm Rescue high-frequency jet ventilation versus conventional ventilation for severe pulmonary dysfunction in preterm infants Cochrane oct 2015 • Existing evidence does not support the use of rescue high-frequency jet ventilation compared with conventional mechanical ventilation for treatment of preterm infants with severe pulmonary problems
  39. 39. AS RESCUE THERAPY Term • High frequency oscillatory ventilation versus conventional ventilation for infants with severe pulmonary dysfunction born at or near term cochrane may 2009 There are no data from randomized controlled trials supporting the use of rescue HFOV in term or near term infants with severe pulmonary dysfunction.
  40. 40. HFJV VS HFOV • High frequency jet ventilation versus high frequency oscillatory ventilation for pulmonary dysfunction in preterm infants Cochrane database May 2016 • no evidence to support the superiority of HFJV or HFOV as elective or rescue therapy

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